Objective— Chronic therapy with synthetic glucocorticoids has been associated with cardiovascular side effects, although differential interindividual susceptibility to glucocorticoids has been observed. The objective of this study was to identify the molecular mechanisms leading to differential glucocorticoid responses in endothelial cells. Approach and Results— We tested the sensitivity of 42 human umbilical vein endothelial cells (HUVECs) to dexamethasone as determined by changes in gene expression, promoter transactivation, and procoagulant activity. We identified that 16 HUVECs were sensitive in every test, 14 HUVECs were sensitive in at least 1 test and 12 HUVECs were resistant in every test to dexamethasone. Nuclear translocation assays revealed that Dex-sensitive HUVECs have higher basal and Dex-stimulated levels of nuclear glucocorticoid receptor compared with Dex-resistant HUVECs. Cycloheximide assays revealed that Dex-resistant HUVECs have significantly shorter glucocorticoid receptor protein half-lives than Dex-sensitive HUVECs. Dex-resistant HUVECs have a stronger interaction of glucocorticoid receptor with the proteasomal recruiting protein, BCL2-associated athanogene 1 (BAG1), as shown by immunoprecipitation assays. Silencing BAG1 expression increased Dex-sensitivity in resistant HUVECs, whereas BAG1 overexpression decreased Dex-sensitivity in sensitive HUVECs. Finally, Dex-resistant HUVECs presented higher BAG1 expression than Dex-sensitive HUVECs. Conclusions— In vitro endothelial sensitivity to Dex varies within individuals and is inversely proportional to BAG1 protein expression and glucocorticoid receptor protein turnover.